1. Field of the Invention
This invention relates to wrist reconstruction and, more particularly, to a method of reconstructing a patient's wrist utilizing a prosthesis with cooperating proximal and distal assemblies.
2. Background Art
Wrist reconstruction is commonly performed to repair the wrist region that may be damaged due to degenerative arthritis and/or from a specific injury. Injuries and/or arthritis may compromise the small carpal bones that make up the wrist, the radius, and/or the ulna. Cartilage is located between the carpal bones and, when intact, guides generally pain-free movement between the carpal bones as an individual moves his/her wrist through various distinct motions. Deterioration of this cartilage may result in direct bone-on-bone contact, which can cause pain severe enough to warrant reconstructive surgery involving the use of a prosthesis.
There are a great number of complications associated with existing wrist prostheses. These complications are due mainly to the conventional manner of fixation of a distal assembly at the carpal region. Typically, a large carpal bone resection is performed and a distal component is inserted with a distal fixation made by two or three screws or prongs in the residual carpus and metacarpus.
In FIG. 1 an exemplary, conventional resection is depicted on a hand 10 shown in relationship to a portion of an individual's ulna 12 and radius 14. A significant portion of the first carpal row (including scaphoid, lunate and triquetrum carpal bones) is resected, with a separation border indicated by the line L. This resection normally involves the removal of a substantial portion of a stable volume of the scaphoid carpal bone 16, the lunate carpal bone 18, and the triquetrum carpal bone 20.
The distal assembly fixed to the remaining portion of the resected bone region is subjected to distraction forces when strains are produced on the hands and to rotational forces, with there being a resulting possibility of loosening of the screws and/or breakage of the bones where the screws are inserted. These prostheses are used primarily for patients with rheumatoid arthritis and rarely post-traumatic wrist destruction from osteoarthritis.
Existing wrist prostheses generally have a common design with a distal fixation on the carpus and metacarpus using different types of screws and prongs fixed in a direction longitudinally, i.e., generally parallel to the length of the individual's radius. They all share a great deal of complication due to this fixation because of the distracting forces applied to the component, among which are: breakage of the prosthesis; fracture of the metacarpal; loosening of the screws; etc.
Further, since a significant stable volume of the carpal bones is removed to accommodate the prosthesis, in the event that the prosthesis fails, a very difficult arthrodesis may become necessary.
The industry continues to seek prostheses that are durable and long-lasting, and which do not require any substantial reconfiguration of the stable existing bone structure that might complicate follow-up procedures in which partial or full reconstruction take place.